Method of heating a substrate with multiple selectively deactuated heaters

ABSTRACT

A substrate heating apparatus having a housing forming a substrate receiving chamber and a heater located inside the chamber. The heater has a thin film flat ribbon heater element sandwiched between two glass-ceramic panels.

This application is a divisional of copending application applicationSer. No. 08/882,367 filed on Jun. 25, 1997.

BACKGROUND OF THE INVENTION

1. Field of The Invention

The present invention relates to a substrate heating apparatus and, moreparticularly, to a heater used in a substrate heating apparatus.

2. Prior Art

U.S. Pat. No. 4,903,754 discloses a heating plate with winding heatingwires. U.S. Pat. No. 4,919,614 discloses a heater in a heat transmittingmember. PCT patent publication No. WO 95/16800 discloses lamp heaters.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a substrateheating apparatus is provided comprising a housing and a heater. Thehousing forms a substrate receiving chamber. The heater is locatedinside the chamber. The heater comprises a heater element sandwichedbetween two glass-ceramic panels. The glass-ceramic panels may besupported by a metal frame. The top panel is preferably partiallycovered by a metal shield which holds stand-off supports for thesubstrate.

In accordance with another embodiment of the present invention asubstrate heater is provided comprising a ceramic heat transfer element,a thin film ribbon heater element, and standoffs. The thin film ribbonheater element is attached directly to the ceramic heat transferelement. The standoffs are connected to the ceramic heat transferelement to support a substrate on the ceramic heat transfer element.

In accordance with another embodiment of the present invention, asubstrate heating apparatus is provided comprising a housing, a topheater, and a bottom heater. The housing forms a substrate receivingchamber. The top heater is connected to the housing in the chamber. Thebottom heater is connected to the housing in the chamber. The top heateris a different type of heater than the bottom heater in bothconstruction and the deliverable quantity of heat possible. Thesubstrate resides between the top and bottom heaters. Between the topheater and the substrate there is preferably a shutter mechanism thatcontrols the amount of radiant heat transferred from the top heater tothe substrate. The heater elements of the top heater are preferably of acoil design.

In accordance with one method of the present invention, a method ofheating a substrate in a substrate heating apparatus is providedcomprising steps of positioning the substrate in a chamber of thesubstrate heating apparatus below a top heater and above a bottomheater, the substrate being located on standoffs on the bottom heater;heating the substrate from heat generated by the top heater; andstopping the heating of the substrate from heat generated by the topheater and continuing heating of the substrate from heat generated bythe bottom heater. This provides for rapid rise-time of the substrateand sustained temperature uniformity after achieving set pointtemperature

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and other features of the invention are explainedin the following description, taken in connection with the accompanyingdrawings, wherein:

FIG. 1 is a schematic cross-sectional view of a substrate heatingapparatus attached to a substrate transport chamber;

FIG. 2 is a schematic cross-sectional view of one of the heaters used inthe substrate heating apparatus shown in FIG. 1;

FIG. 3 is a top plan view of the heater shown in FIG. 2;

FIG. 4 is a top plan view of the thin film ribbon heater element used inthe heater shown in FIG. 3;

FIG. 4A is an enlarged view of one of the loops of the heater elementshown in FIG. 4;

FIG. 5 is an enlarged cross-sectional view of a portion of the heatershown in FIG. 3; and

FIG. 6 is a schematic cross-sectional view of an alternate embodiment ofa substrate heating apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is shown a schematic cross-sectional view ofa substrate heating apparatus 10 incorporating features of the presentinvention attached to a substrate transport chamber 12. Although thepresent invention will be described with reference to the embodimentsshown in the drawings, it should be understood that the presentinvention could be embodied in many different alternate types ofembodiments. In addition, any suitable size, shape or type of elementsor materials could be used.

The substrate heating apparatus 10 is part of a substrate processingapparatus 14 which includes a transport 16 having the transport chamber12 and a plurality of processing modules (not shown) attached to thetransport chamber 12. An example of a substrate processing apparatus canbe seen in U.S. Pat. No. 4,715,921 which is hereby incorporated byreference in its entirety. The substrate processing apparatus 14 isadapted to process substrates, such as semi-conductor wafers or panelsfor flat panel displays. The transport 16 includes a robot arm 18 withan end effector 20. The robot arm 18 is adapted to move substrates intoand out of the processing modules and the heating apparatus 10. Inalternate embodiments, any suitable type of substrate transport could beused and, the substrate heating apparatus 10 could be used in anysuitable type of substrate processing apparatus.

The substrate heating apparatus 10 includes a housing 22, a plurality ofheaters 24, and an elevator mechanism 26. The housing 22 is attached tothe transport chamber 12 and has an entrance 28 into its chamber 30.Preferably, a door is located at the entrance 28 to seal off the chamber30 from the transport chamber 12. The heaters 24 are located in thechamber 30 and are attached to an elevator arm 32 of the elevatormechanism 26 for movement up and down in the chamber 30 as illustratedby arrow A. In an alternate embodiment, the substrate heating apparatuscould be a single substrate heater. In addition, the substrate heatingapparatus need not have an elevator mechanism. The apparatus 10 ispreferably used as a pre-heat and degas module.

Referring also to FIG. 2, a schematic cross-sectional view of one of theheaters 24 is shown. In this embodiment the heater 24 includes a frame34, two heat transfer members 36, 37, and a heater element 38. The frame34 has a bottom member 40 and a top rim shield 42. Referring also toFIG. 3, the rim shield 42 has support webbing 44 with standoffs 46thereon. The standoffs 46 are adapted to support the substrate on top ofthe heater 24. The majority of the rim shield 42 is open to allowradiant heat to travel directly from the top heat transfer member 36upward towards the substrate on the standoffs 46. The rim shield 42 andbottom member 40 capture the other members therebetween. Preferably, theframe 34 is comprised of stainless steel. The bottom member 40 ispreferably substantially open to allow heat to travel downward from theheater 24.

The two heat transfer members 36, 37 have a general panel shape and arepreferably comprised of ceramic. In particular, the members 36, 37 arepreferably comprised of glass-ceramic material. Glass-ceramics arepolycrystalline solids produced by the controlled crystallization ofglasses. In a preferred embodiment the glass-ceramic panels are about0.2 inch thick, but any suitable thickness could be used. In a preferredembodiment, the panels 36, 37 measure about 29 inches by 25 inches, butany suitable size could be provided. The glass-ceramic panels need notbe rectangular. They could be circular or have any other suitable shape.The glass-ceramic material has been selected for the panels 36, 37because, among other things, of its high radiation emissivity (about0.8). It has also been discovered that the glass-ceramic material isparticularly well suited for heaters of relatively large sizesubstrates, such as more than 20 inches in width and/or length, becauseof the low thermal expansion of glass-ceramic material. Located betweenthe two glass-ceramic panels 36, 37 is the heater element 38. Referringalso to FIG. 4, the heater element 38, in the embodiment shown, is athin film flat ribbon heater. The ribbon heater 38 is made ofelectrically conductive metal with a preferred thickness of about0.004-0.005 inch. The pattern shown is formed by etching away unwantedmetal from a flat thin sheet. The pattern includes securing holes 48,electrical contact mount areas 50, 52, a thermocouple clearance area 54,and a non-uniform pattern of serpentine looped sections. Two electricalcontacts 56, 58 (see FIG. 3) are attached to the ribbon heater 38 at theelectrical contact mount areas 50, 52 and extend out of the lateral sideof the heater 24. A thermocouple 60 is located in the area 54 and alsoextends out of the lateral side of the heater 24. The rim shield 42helps to protect the thermocouples from thermal cross-talk between anytwo adjacent heaters. The two glass-ceramic panels 36, 37 have recessesthat physically locate and support the heater element and thermocouple.

The pattern of the ribbon heater 38 has been designed to provide asubstantially uniform heating of the substrate. The width of the metalin the strips that form the serpentine loops and the spacing betweenadjacent metal strips has been selected to provide different powerdensity zones of heat generation. A center zone B has relatively widestrips and relatively wide spacing between adjacent strips. Anintermediate zone C, which surrounds the center zone B, has varyingstrip width and spacing. The thinner the strip width the greater theelectrical resistance. Thus, thinner strip width results in greater heatgeneration than wider strip width. The outer loop has side zones D andcorner zones E. The corner zones E have the smallest width stripsbecause heat loss will be greatest at the corners of the heater. Thus,the greatest heat generation is required at the corners in order toprovide uniform heating of the substrate from the heater. Referring alsoto FIG. 4A, an enlarged view of one of the loops in one of the sidezones D is shown. Most of the loops include a pair of loop strips 29a,29b. A gap 31 separates the strips 29a, 29b. In zones C and D, thestrips 29a, 29b have outer sections with thin strip widths F and innersections with thicker strip widths G. Thus, in most of the loops inzones C and D, more heat is generated at the outer part of the loop(nearest to the perimeter edge of the element 38) than at the inner partof the loop. Thus, loops in the zone C have different inner and outerheat generation and loops in the zone D have different inner and outerheat generation. Other variations could be provided so long as the totalheat output from the heater is a preferable uniform heating from the topsurface of the plate 36 to the substrate. Uniform heating provides theadvantage of reducing risk of non-uniform processing of the substrateafter it leaves the heating chamber. This becomes increasingly importantfor large substrates, such as 20 inches or more in width and/or length,which will demand more from the heating system to provide uniformity.The unique shape of the pattern of the ribbon heater 38 allows theheating of substrates in vacuum or gas environments to temperatures ofup to about 500° C. with very precise temperature uniformity. Theheating allows impurities, such as water vapor, to be heated off of thesubstrate and removed by means of vacuum pumping in the degas process.In alternate embodiments, the pattern of the ribbon heater, includingvariations in conductor strip width and strip density, can be designedor varied based upon such variables as the shape of the substrate, theshape of the heater, and the expected or desired pattern of emission ofheat from the heater to the substrate. In the present embodiment, theribbon heater 38 was designed to heat a rectangular flat panel displaysubstrate. Thus, heat generated from zone B needs to be less than heatgenerated from the other zones because less heat loss occurs in thecenter as compared to outer areas. The serpentine loops of the strips inall the zones B, C, D, E was selected to maximize strip density, but notmake the strips so small as to inadvertently tear during assembly withthe glass-ceramic panels 36, 37.

Referring also to FIG. 5, a schematic cross-section of the panels 36, 37and ribbon heater 38 is shown. The two panels 36, 37 sandwich the ribbonheater 38 therebetween. The panels 36, 37 have pin recesses 62, 63 thatface each other. Mounting washer pins 64 are located in the recesses 62,63 and in the mounting lugs 48 of the ribbon heater 38. These recessesand mounting lugs are strategically located across the heater to alignthe assembly and keep it assembled. In alternate embodiments, othertypes of means for aligning and retaining the assembly could be used.

Previous practice in the semiconductor industry has used either metalplate heaters or heating lamps to heat and degas substrates. In the caseof a large flat panel display substrate, metal plate heaters were notpractical because they were limited in the upper temperature achievableand, lamps were difficult to regulate for both set point temperature andsubstrate temperature uniformity. The heater described above providesfor a tailored heat distribution across the top surface of the heater.In addition, the use of ceramic material provides high heat transferrates when radiation is the only heat transfer medium possible, such aswhen the chamber 30 is maintained in a vacuum. Radiation emissivity canbe as high as 0.8. This is about twice the emissivity one would expectin a metal plate heater. The location of the thermocouple directlybetween the plates 36, 37 can provide an accurate temperaturemeasurement for controlling electrical power supply to the heaterelement 38. No adhesives or hardware are necessary to contain the heaterelement because the washing pins 64 lock the panel/heater elementassembly together with the frame 34 completing the sandwich assembly. Inalternate embodiments, the panels 36, 37 could be made of alternativematerials such as other types of ceramics, glass and/or metal. If onlytop side heating from the heater is desired, the bottom member 40 of theframe 34 could be enclosed and insulated. The panels 36, 37 could alsobe made of dissimilar materials from each other. In other alternateembodiments, different types of heating elements could be used, such asa calrod. Because a calrod has its own electrical ceramic insulation,the calrod could be used directly on a metal heat transfer panel.However, the calrod needs to have a non-uniform serpentine pattern inorder to provide a tailored substantially uniform heat distributionacross the top surface of the heater. If the calrod is used with aglass-ceramic panel, the panel could have a calrod receiving groovealong one of its sides to receive the calrod.

Referring now to FIG. 6, an alternate embodiment is shown. In thisembodiment a substrate heating apparatus 70 is provided with a housing71 having a chamber 72, a top heater 74, and a bottom heater 24. Thesubstrate S is positioned in the chamber 72 on the standoffs 46. Morespecifically, the substrate S is positioned below the top heater 74 andabove the bottom heater 24. The top heater 74 is a different type ofheater than the bottom heater 24. In this embodiment the top heater 74comprises a ceramic plate 75 into which grooves are cut to provide apattern for a wire coil type heating element 76. However, in alternateembodiments other types of heaters could be used. The apparatus 70 isspecifically configured to provide a two step heating method. The topheater 74 is turned ON to provide a relatively quick temperatureincrease in the substrate. As the substrate quickly approaches its setpoint temperature, the top heater element is turned OFF and a set ofvanes 77 of a shutter system is moved to a closed position. A motor 80is connected to the vanes 77 to move the vanes between open and closedpositions. However, any suitable type of drive system could be used. Inaddition, a shutter between the top heater and the substrate need not beprovided. The vanes 77, in their closed position, block the top heaterfrom the substrate. The bottom heater 24 is also turned ON. The bottomheater 24, which is designed to operate near the set point temperaturecan provide uniform heat transfer to the substrate S and continue toraise the temperature of the substrate S to its final desiredtemperature. This two step method provides the benefits of relativelyfast speed heating from the top heater 74 and the controllability anduniformity of heat from the bottom heater 24 in the single apparatus 70.In an alternate embodiment, the heater 24 could be located on top of thesubstrate and a different type of heater could be located below thesubstrate. In another alternate embodiment, the apparatus could have twoof the heaters 24; one above the substrate and one below the substrate.Other different types of heaters could also be used. Turning the top andbottom heaters ON and OFF and moving the vanes 77 between open andclosed positions are preferably controlled by computer. The control maybe based upon time that the top heater 74 is ON or a temperature sensor,as well as signals from the thermocouple in the bottom heater 24.

It should be understood that the foregoing description is onlyillustrative of the invention. Various alternatives and modificationscan be devised by those skilled in the art without departing from thescope of the present invention. Accordingly, the present invention isintended to embrace all such alternatives, modifications and varianceswhich fall within the scope of the appended claims.

What is claimed is:
 1. A method of heating a substrate in a substrateheating apparatus, the method comprising steps of:positioning thesubstrate in a chamber of the substrate heating apparatus below a topheater and above a bottom heater, the substrate being located onstandoffs on the bottom heater; heating the substrate from heatgenerated by the top heater; and stopping the heating of the substratefrom heat generated by the top heater and continuing heating of thesubstrate from heat generated by the bottom heater.
 2. A method as inclaim 1 wherein the step of stopping comprises moving vanes locatedbetween the top heater and the substrate to a closed position.
 3. Amethod as in claim 1 further comprising heating the substrate from heatgenerated by the bottom heater during heating of the substrate by thetop heater.
 4. A method as in claim 1 further comprising providing thetop and bottom heaters as different types of heaters.
 5. A method as inclaim 1 wherein the step of stopping the heating of the substrate fromheat generated by the top heater comprises reducing heat output from thetop heater as the substrate approaches a final desired set pointtemperature.
 6. A method as in claim 5 wherein the step of reducing heatoutput from the top heater comprises turning OFF a heater element in thetop heater.
 7. A method as in claim 5 wherein continuing heating of thesubstrate from heat generated by the bottom heater raises thetemperature of the substrate to its final desired set point temperature.8. A method as in claim 1 wherein continuing heating of the substratefrom heat generated by the bottom heater comprises the bottom heaterhaving a thin film ribbon heater element attached directly to a ceramicheat transfer element, and wherein the thin film ribbon heater generatesheat which is transferred to the substrate through the ceramic heattransfer element.
 9. A method as in claim 8 wherein the thin film ribbonheater element comprises serpentine looped sections arranged in apattern of at least two concentric general ring sections with differentthicknesses for generating different heat outputs from each general ringsection.
 10. A method as in claim 8 wherein the thin film ribbon heaterelement comprises loops having outer thin sections and inner thickersections for generating different heat outputs from the differentsections of each loop.
 11. A method of heating a substrate in asubstrate heating apparatus, the method comprising steps of:positioningthe substrate in the substrate heating apparatus between a first heaterand a second heater of the apparatus; heating the substrate from heatgenerated by the first heater; and reducing heat generated by the firstheater and continuing heating of the substrate from heat generated bythe second heater.
 12. A method as in claim 11 further comprisingheating the substrate from heat generated by the second heater duringheating of the substrate by the first heater.
 13. A method as in claim11 further comprising providing first and second heaters as differenttypes of heaters.
 14. A method as in claim 11 wherein the step ofstopping the heating of the substrate from heat generated by the firstheater comprises reducing heat output from the first heater as thesubstrate approaches a final desired set point temperature.
 15. A methodas in claim 14 wherein the step of reducing heat output from the firstheater comprises turning OFF a heater element in the first heater.
 16. Amethod as in claim 14 wherein continuing heating of the substrate fromheat generated by the second heater raises the temperature of thesubstrate to its set point temperature.
 17. A method as in claim 11wherein continuing heating of the substrate from heat generated by thesecond heater comprises the second heater having a thin film ribbonheater element attached directly to a ceramic heat transfer element, andwherein the thin film ribbon heater generates heat which is transferredto the substrate through the ceramic heat transfer element.
 18. A methodas in claim 17 wherein the thin film ribbon heater element comprisesserpentine looped sections arranged in a pattern of at least twoconcentric general ring sections with different thicknesses forgenerating different heat outputs from each general ring section.
 19. Amethod as in claim 17 wherein the thin film ribbon heater elementcomprises loops having outer thin sections and inner thicker sectionsfor generating different heat outputs from the different sections ofeach loop.
 20. A method of heating a substrate in a substrate heatingapparatus, the method comprising steps of:positioning the substrate inthe substrate heating apparatus between a first heating and a secondheater; outputting heat from the first heater at a first rate to heatthe substrate; outputting heat from the second heater at a second rateto heat the substrate, wherein the first rate of heat output is largerthan the second rate of heat output; and reducing heat output from thefirst heater as a temperature of the substrate approaches a desiredfinal set point temperature and continuing heating of the substrate tothe desired final set point temperature by the second heater.
 21. Amethod as in claim 20 wherein the step of reducing heat output from thefirst heater comprises turning the first heater OFF.